1. Field of the Invention
The present invention relates to an image forming apparatus, such as an electrophotographic copying machine, and a laser beam printer. More particularly, the invention relates to the improvement of an image forming apparatus constructed such that a toner image formed on an image bearing body, e.g., a photo-receptor drum, is temporarily transferred onto an intermediate transfer body, and then the toner image is transferred from the intermediate transfer body to a recording sheet.
2. Description of the Related Art
Generally, in the image forming apparatus, such as the electrophotographic copying machine or the laser beam printer, a toner image is formed on the surface of a photo-receptor drum in accordance with image data, the toner image is transferred onto a recording sheet, and the toner image transferred is fused and fixed on the recording sheet. Recently, some type of the full-color copying machine or full-color laser beam printer is known. In this type of the machine, formed on the photo-receptor drum is primarily transferred onto the intermediate transfer body. Those color toner images of four colors, yellow, cyan, magenta and black, are superimposed one upon the other to form a composite color toner image. The composite color toner image thus formed is transferred onto a recording sheet thereby to form a full-color image thereon.
A transfer efficiency of the toner image is affected by surface states of the photo-receptor drum and the intermediate transfer body, and resistance variations of the recording sheet and the intermediate transfer body, which results from the temperature and humidity variations. Accordingly, it is difficult to keep the transfer efficiency at 100%. After the transferring of the toner image, residual toner is present on the surfaces of the photo-receptor drum and the intermediate transfer body as the transfer sources of the toner image. To cope with this, cleaning devices are provided downstream of the toner-image transferred parts of the photo-receptor drum and the intermediate transfer body (referred to as xe2x80x9cphoto-receptor drum and the likexe2x80x9d), and remove the residual toner from the photo-receptor drum and the like before the next toner images are formed.
The cleaning device, known and widely used, is such that an elastic rubber blade is pressed against the surface of each of the photo-receptor drum and the like, and the residual toner is mechanically removed by the blade. The cleaning device of the blade type does not need a drive part. Accordingly, it has advantageous features of simple structure and low cost. During the residual toner removing operation, the blade not only removes the toner particles, but also scrapes off the surfaces of the photo-receptor drum and the like as bodies to be cleaned although its scraping amount is extremely small. Damage of the photosensitive layer and the like of the photo-receptor drum, caused by the scraping operation, is great. As a result, the lifetime of the photo-receptor drum and the like is reduced. In particular, recently, there is a tendency of the apparatus size reduction, and in this circumstance, the diameter reduction of the photo-receptor drum and the like is remarkable. Further, there is a tendency of increasing the number of rotation of the photo-receptor drum and the like for a fixed number of print sheets. Accordingly, where the cleaning device of the blade type is employed, the life of the photo-receptor drum and the like is more and more reduced.
For other cleaning devices than the blade type cleaning device, a called fur brush cleaning device is typically known in which a brush roller having a great number of abrasive brushes planted therein is brought into contact with the photo-receptor drum and the like, and the brush roll is rotated at high speed, whereby the residual toner is mechanically removed. The brush roll is driven to rotate by the motor. An efficiency of capturing the toner particles is improved in a manner that a linear velocity ratio of the brush roll to the photo-receptor drum and the like as bodies to be cleaned is selected to be large. In the fur brush cleaning device, the damage of the photo-receptor drum and the like is less than that in the blade type cleaning device. Accordingly, the life of the photo-receptor drum and the like will be increased correspondingly.
In the fur brush cleaning device, the brush roll is in sliding contact with the surfaces of the photo-receptor drum and the like. Accordingly, a called toner cloud in which toner particles flow in the air is easy to be generated. In particular, much toner cloud is generated at both ends of the brush roll. If no measure is taken for the toner cloud, the toner particles attach to the devices within the image forming apparatus. And, the recording sheet being transported within the image forming apparatus is soiled with the toner particles. The toner cloud is discharged out of the image forming apparatus, and will contaminate the air in the room and adversely affects the human body.
In the conventional cleaning device, the abrasive bristles of the brush roll are struck against the flicker bar to thereby forcibly shake the toner particles from the brush roll, and the toner particles are collected. Therefore, there is less chance that the brush roll continues its rotation while holding much toner particles. Recently, the size reduction of the cleaning device progresses, and there is proposed a cleaning device not provided with a toner collecting mechanism (Japanese patent laid-open No. 2001-07544). In this new cleaning device, the brush roll functions to temporarily hold the residual toner particles during the execution of the image forming job so as not to hinder the formation and transfer of the toner images. During the execution of the image forming job, the toner particles held by the brush roll are discharged, at intervals, to the photo-receptor drum and the like, and transported to the roll located downstream as in the case of transferring the toner image. Finally, the toner particles are collected by the cleaning device provided for the final stage roll. For this reason, the brush roll continues its rotation while holding the residual toner having been removed from the photo-receptor drum and the like. Accordingly, much toner cloud is easy to be generated when the brush roll is brought into sliding contact with the photo-receptor drum and the like, when comparing with the conventional cleaning device.
In a method, frequently used, of preventing the inside of the image forming apparatus from being filled with the toner cloud generated in the cleaning device, the brush roll is surrounded by a casing. A sealing member, which comes in contact with the photo-receptor drum and the like, is provided at the edge of the casing thereby to prohibit the toner cloud generated by the sliding of the brush roll from leaking outside the casing. Another frequently used method is that the air around the cleaning device is sucked by a fan, and toner particles are removed from the sucked air by use of a filter.
In the former method, a gap through which the toner cloud leaks is closed by making the sealing member contact with the photo-receptor drum and the like. Therefore, the wear of the photo-receptor drum and the like is problematic, and deterioration of the sealing member per is also problematic. The latter method needs the fan and suction duct, resulting in increase of manufacturing cost, and hindering of the size reduction of the image forming apparatus.
Accordingly, an object of the present invention is to provide an image forming apparatus operable such that even when the brush roll brushes a photo-receptor drum and the like to generate a toner cloud, the apparatus is capable of preventing the toner cloud from diffusing into the image forming apparatus, such as a copying machine or a printer, without using a sealing member of the contact type, a fan for absorbing the toner cloud, and the like, whereby the cleaning of the inside of the machine as well as the reduction of the cost to manufacture is realized.
To achieve the above object, there is provided an image forming apparatus having an image bearing body having a photosensitive layer on the surface thereof, a toner image as defined by image information being formed on the photosensitive layer, an intermediate transfer body to which a toner image is transferred from the image bearing body, a transfer roll device for transferring the toner image from the intermediate transfer body onto a recording sheet, a brush roll device for removing the residual toner from the intermediate transfer body, and a toner collecting device for collecting the toner attached to the surface of the transfer roll device, the improvement being characterized in that an axial length of the intermediate transfer body is longer than that of the brush roll device, and the axial length of each of the transfer roll device and the toner collecting device is longer than that of the intermediate transfer body.
The axial length of the intermediate transfer body of which the residual toner is removed by the brush roll member is longer than that of the brush roll device. A toner cloud generated at both ends of the brush roll device when the brush roll device is rotated, attaches to both ends of the intermediate transfer body which are protruded from the brush roll device, thereby minimizing the diffusion of the toner cloud into the inside of the machine. The axial length of the transfer roll device for transferring the toner image from the intermediate transfer body to the recording sheet is longer than that of the intermediate transfer body. Accordingly, the toner attached to both ends of the intermediate transfer body when it is rotated maybe transferred from the intermediate transfer body to the transfer roll device. Finally, the toner collecting device provided on the transfer roll device collects the toner. Accordingly, the diffusion of the toner cloud generated at both ends of the brush roll device into the image forming apparatus is minimized.
The axial length of the brush roll device is not its axial length including the rotary shaft, but is the axial length of a part of the rotary shaft of the brush roll device at which the abrasive bristles are provided. The reason for this is that the part of the brush roll device at which the abrasive bristles are provided functions as the brush roll device.
The intermediate transfer body for transferring the toner between the image bearing body and the recording sheet does not always consist of one stage of intermediate transfer body. The intermediate transfer body may include a primary intermediate transfer member to which a toner image is primarily transferred from the image bearing member, and a secondary intermediate transfer member to which a toner image is secondarily transferred from the primary intermediate transfer member. In this case, the first brush roll for removing the residual toner is provided on the primary intermediate transfer member, and a second brush roll for removing the residual toner is provided on the secondary intermediate transfer member. To minimize the diffusion of the toner clouds generated at both ends of the first and second brush rolls into the inside of the image forming apparatus, the axial length of the primary intermediate transfer member must be longer than that of the first brush roll, and the axial length of the secondary intermediate transfer member must be longer than that of the second brush roll. In order that when the toner attached to both ends of the primary intermediate transfer member is transferred to the secondary intermediate transfer member, the toner is reliably removed from the secondary intermediate transfer member, the axial length of the second brush roll must be longer than that of the primary intermediate transfer member.
In implementation of the invention, the brush roll device (referred to as a refresher brush), like that of the intermediate transfer body, is provided for the image bearing body. The toner attached onto the image bearing body is removed by use of the refresher brush. To suppress the toner cloud generated at both ends of the refresher brush from diffusing into the image forming apparatus, The axial length of a photosensitive layer formed on the surface of the image bearing body is longer than that of the refresher brush, and the axial length of the intermediate transfer body is longer than that of the photosensitive layer. The reason why the axial length of the photosensitive layer is discussed as a great matter in the specification follows. If the photosensitive layer having such a length is used, a potential gradient may be formed between the photosensitive layer and the intermediate transfer body. If so done, the transfer of the toner that is attached, in the form of toner cloud, to both ends of the image bearing body to the intermediate transfer body may be suppressed to some degree.